A New Device for In Vivo Environment-Simulating Confined-Condition Soft Tissue Creep Recovery Studies

Abstract In biomechanical research, accurately simulating the natural mechanical environment of articular cartilage is crucial for studying its biomechanical behavior. However, constrained by the altered properties of ex vivo biological cartilage, precisely simulating the creep response of cartilage under physiological loads remains a significant challenge in the field of tissue engineering. This study developed a confined creep device simulating in vivo conditions, integrating a servo-controlled uniaxial testing machine with high-resolution digital image correlation (DIC) to achieve noncontact three-dimensional deformation tracking, thereby enabling systematic evaluation of the creep recovery properties of cartilage. The closed-loop control system of this apparatus, featuring a downward-acting actuator and pressure/displacement sensing mechanism, ensures precise and stable detection under the optical imaging and mechanical testing. The liquid environment within the confines of the system mitigates errors arising from the time-dependent nature of biological samples and individual variations. The effectiveness of the device in reconstructing the internal mechanical environment in vitro was further verified by comparing the creep recovery behavior of the pig articular cartilage samples in a confined liquid environment with those in a nonconfined nonliquid environment. The confined environment simulates the in vivo conditions, enabling cartilage tissue to exhibit significantly superior creep performance (33±0.64% versus 55±0.76% strain accumulation, p < 0.05), and deformation recovery property, closely replicating natural mechanical behavior. This method provides an innovative platform for investigating the in vivo cartilage creep mechanisms and shows potential for optimizing tissue-engineered scaffolds.